Hrm if I remember my electronics correctly you'll need a TIP31(3A) transistor or TIP120(8A) transistor. Also an old molex(female) power connection, 3.5mm jack and splitter, solder iron, solder, flux, wire and your LEDs also preferably a DIY pcb board. I made a quick diagram instead of trying to explain it. I'd test it out somehow first like using an old set of speakers with a headphone jack and an old psu or power brick for power just in case you have something shorted out it won't harm you main system.

Hope this helps.

Oh, the geniuses on HWC. Looks simple enough for me to do. I actually heard about the TIP31 before and I forgot all about it. Thanks for this.